Initialization by FE solution: operation

Starting by FE solution

It is possible to start a transient computation by using as initial state the result of a Magneto Static, an AC Steady-State Magnetic or a Transient Magnetic problem.

AC Steady-State - Transient Magnetic relevance / example

The AC Steady-State application permits the study of the steady state regime, but it has the following drawbacks:

  • approximations in the taking into consideration of the magnetic saturation*
  • no possibility to compute the harmonics in space and time

The Transient Magnetic application compensates for the limits quoted above, but it has the drawback of requiring a computation time that can be quite long. Then, the number of time steps is important.

Starting a Transient Magnetic application on the basis of the AC Steady-State solution permits to rapidly reach the steady state regime without being forced to solve all the time steps of the Transient Magnetic problem until the steady state regime is reached.

Remember: *With an AC Steady-State Magnetic application, the approximations are carried out in order to take into consideration the non linear materials. Flux deal then with the equivalent B(H) characteristics (B sinus, H sinus…). The local values obtained with such equivalent curves get more or less accurately close to the real result (Example of the asynchronous machine).

Transient Magnetic - Transient Magnetic relevance / example

As with an AC Steady-State application, the Transient Magnetic application permits to obtain the steady state regime more rapidly without the need for the user to make again the computation of the transient phases or those for start-up (starting up of a synchronous machine with magnets, for instance).

It also permits to reach a certain specified point of the steady state regime – for example the passage at zero of the current of one of the phases of an electric alternator.

Finally, and mainly, it gives the possibility of an initialization by FE problem when the system comprises permanent magnets, which is not possible with an initialization by an AC Steady-State problem.


The operation principle is described in the table below in the case of an AC Steady-State – Transient Magnetic sequence.

Phase Description
1 Construction of the Flux project 1 (AC Steady-State application)
2 Solving of the Flux project 1 (AC Steady-State application)

Export of the FE solution:

Creation of an exchange file (format FTS): see this page for more information on the phase choice

Phase Description

Construction of the Flux project 2 (Transient Magnetic application) on the basis of the Flux project 1 (AC Steady-State application)

During the construction of the Transient Magnetic project, be careful to repeat the same phases defined in the corresponding sources in the electrical circuit of the AC Steady-State project.
In general, the projects (1 and 2) must be strictly identical from different points of view:
  • geometrical (same dimensions);
  • mesh;
  • physical (same materials used by the same regions, mechanical sets ...);
  • and the electrical circuit (same components, name of the components, same phases and same maximal values on the same circuit sources ...).

Choice of the initial conditions:

  • Initialization of the type "by file"
  • Import of the .FTS file created during step 3 here above
3 Solving of the Flux project 2 (Transient Magnetic application)